Therm-Control Low-Temperature Protection Logic - Viessmann VITOROND 200 VD2A-125 Installation Instructions Manual

General Information

Therm-Control Low-Temperature Protection Logic

Therm-Control is an integrated low-temperature protection
logic provided by the Vitotronic control.
The control uses a Therm-Control temperature sensor
specifically positioned in the casting close to the boiler
return (shown on page 9 and 31) to capture the thermal
state of the boiler (i.e. the temperature of the system
return mixed with the boiler water) and react as early
as possible. The Therm-Control Logic shuts off the system
pump (and, if applicable, closes the mixing valve) and
brings the burner to full fire until the boiler minimum
setpoint temperature is reached during start-up,
preventing the formation of flue gas condensation and
allowing for maximum heat transfer to the system.
This ensures steady supply temperatures with only
minimal fluctuations, and eliminates the need for a shunt
pump or return temperature elevation provided by a
Low Temperature Protection (LTP) Package.
10
Vitorond 200, VD2A Series Installation
Example:
Take a heating system with one heating circuit and
a mixing valve.
In the start-up phase, the set Therm-Control temperature
is not achieved at the Therm-Control sensor.
The mixing valve downstream of the boiler receives
a signal via the control to reduce the flow rate and to
operate the burner at full fire (Phase 1).
The boiler temperature and that captured by the Therm-
Control sensor now rapidly rise. The mixing valve opens
when the set temperature is exceeded at the Therm-
Control sensor, and the flow rate (in this example 50%)
inside the boiler is steadily increased (Phase 2).
The return water temperature rises after a certain time
has elapsed which is a function of the system water
volume. As the return temperature rises, the mixing
valve opens further until the maximum flow rate (100%
in Phase 3) is achieved. Now the control will modulate
the burner firing rate to achieve the required setpoint
(burner modulation), and weather-responsive boiler water
temperature modulation will take place.